Flushing your DNS cache in Mac OS X is actually really easy, and there are two different commands to use, one for Leopard and for Tiger. Depending on your version of OS X, open your Terminal and follow the appropriate directions below:
Flush DNS Cache in Mac OS X 10.5, Mac OS X 10.6, or OS X 10.7 Lion
Launch Terminal and issue the following command:
All done, your DNS has been flushed. On a side note, the dscacheutil is interesting in general and worth taking a look at, try the -statistics flag instead for some stats.
Flush your DNS Cache in Mac OS X 10.4 Tiger
Type the following command in the Terminal:
That’s it, that’s all there is to it.